OF-2539: Improve naming of threads
This overrides the default name (pool-x-thread-y) used for threads generated by an executor service to something that is more identifiable. Should not introduce functional changes.
OF-2543: When retrieving pubsub items, always include payload
The pubsub node configuration option `pubsub#deliver_payloads` is defined in XEP-0060 to control if payloads are included in pubsub notification events. Openfire should not use it to determine if payloads are to be included when answering item retrievals (those should _always_ have payloads, if they exist on the item).